code: def helper_test_shape_equality(self, metric):
      assert (
          round(
              abs(
                  metric(self.series12, self.series21)
                  - metric(
                      self.series1.append(self.series2b),
                      self.series2.append(self.series1b),
                  )
              ),
              7,
          )
          == 0
      )
  
imports: import numpy
  import pandas
  import pytest
  from darts import TimeSeries
  from darts.metrics import metrics
label_desc: Use image node_id 3 for calling the TestMetrics obj's underlying member method code with example usage: obj.helper_test_shape_equality(metric) without return types